### Use of Confidence Intervals and Sample Size Determination

The Modulus of rupture (MOR) for a particular grade of pencil lead is known to have a standard deviation of 250 psi. a. A random sample of 16 pencil leads yielded a sample mean of 6490. Construct a 90% confidence interval for the true mean MOR. b. Find the sample size required to estimate the true mean MOR to within ± 100 u